Root Rot Pathogens of Wheat in South Dakota and Their Affect on Seed Germination and Seedling Blight in Spring Wheat Cultivars

Crown rot and common root rot are the important root diseases in wheat (Triticum aestivum L.) and other cereals causing significant germination and yield losses in the Northern Great Plains and other parts of the world. Bipolaris sorokiniana (Bs) and Fusarium graminearum (Fg) cause common root rot and crown rot respectively, are the important wheat root pathogens that can affect seed germination, seedling establishment and impact crop productivity. A survey was conducted in the year 2014 and 2015 to study the distribution and the prevalence of root rot pathogens in South Dakota. Out of 31 and eight roots samples collected in 2014 and 2015, respectively, F. graminearum was the major pathogen recovered in both years. All the collected samples harbored F. graminearium, and 50% of the samples produced B. sorokiniana. In 2014, 125 isolates of F. graminearum and 62 isolates of B. sorokiniana were recovered from 31 root samples and in 2015, 38 isolates of F. graminearum and eight isolates of B. sorokiniana were recovered from eight root samples. The fungus Gaeumannomyces graminis tritici associated with Take-all was not recovered from the collected samples in both years. Further, we studied the effect of B. sorokiniana and F. graminearum infested seed on germination and seedling establishment (blight) of 11 HRSW wheat cultivars under greenhouse and field conditions (Brookings and Volga). Seeds of 11 hard red spring wheat cultivars HRSW cultivars, Advance, Brick, Briggs, Forefront, Oxen, Prevail, Russ, Select, SD4189, SD4215, and Traverse were infested individually with B. sorokiniana and F. graminearum by spraying with their respected spore suspension. Infested seed from all 11 cultivars were planted in paper cups (10 seeds/cup) filled with sterile vermiculite, using a complete randomized design. Seed germination and seedling blight data was recorded 10 and 20 days’ post planting. The percent germination losses when the seed was infested with F. graminearum ranged from 4 to 33% while the seedling survival rate of the cultivars varied from 48 to 87% and the seedling blight ranged from 7-27% but when seed was infested with B. sorokiniana, percent germination varied from 2-17% with 58 to 96% seedling survival rate and 0-16% seedling blight. We further, planted 100 seeds of seven (2015) and 11 (2016) HRSW cultivars with six different treatments in a split plot design experiment in three replications at two field locations, Brookings and Volga. The treatments included were uninfested seed + untreated (T1), unifested + treated with fungicide (T2), infested (B. sorokiniana) + treated (T3), infested (B. sorokiniana) + untreated (T4), infested (F. graminearum) + treated (T5), infested (F. graminearum) + untreated (T6). Seed germination and seedling blight data were recorded after the germination for three consecutive weeks. Wheat cultivars varied in seed germination and seedling blight to both the pathogens; however, low seed germination was observed in F. graminearum infested seed as compared to B. sorokiniana infested seed at both locations in both years. Cultivars Russ (72%) and Oxen (80%) were highly affected for seed germination and seedling blight to both pathogens whereas Forefront (92%), Select (95%) and Briggs (88%) had the highest germination and the higher seedling survival rate as compared to the other cultivars both under greenhouse and field conditions. The percent germination losses when the seed was infested with F. graminearum ranged from 17-35% while the seedling survival rate of the cultivars varied from 92-99%. In case of the seed infested with B. sorokiniana, germination losses ranged from 2-15% with the only highest germination loss observed in Russ cultivar (32%) with the survival rate of all the cultivars ranged from 91-97%. Fungicide treatment (T3 and T5) significantly increased the seed germination from 14-37% and the seedling blight was also reduced in almost all the cultivars. In another experiment, where oat kernels were used as a source of inoculum, reduction in percent seed germination was observed however, it was not significant